1. Field of the Invention
The present invention relates to a molding apparatus. More particularly, the present invention relates to a molding apparatus for molding optical lenses and precision mold objects having the least face-tilting problem.
2. Description of the Related Art
With the rapid development of electronic technologies in recent years, the functions of various type of optical electronic products including cameras, digital cameras, camcorders, facsimiles, printers, optical disc players, scanners and projectors continue to improve while their prices continue to drop. These electronic products are so popular that they have almost become indispensable to us in out daily life.
Most optical products have at least one precision optical device that incorporates an optical lens, for example. Optical lenses can be roughly divided into spherical lenses and aspheric lenses. At present, most spherical optical lenses are fabricated by grinding while most aspheric lenses are fabricated by molding.
FIG. 1 is a schematic cross-sectional view showing the structure of a conventional molding apparatus for molding optical lenses. As shown in FIG. 1, a conventional lens molding apparatus 100 mainly comprises a cylindrical mold 110 and an internal cavity 150 formed by an upper mold core 120 and a lower mold core 130. A gob is disposed inside the mold cavity 150. Through a process of heating the mold to a high temperature, the gob is softened and molded into the required shape. After a period of cooling, an optical lens 54 is formed inside the mold. In the process of converting the gob into a molded lens 54, the central axis C1 of the upper mold core 120 and the central axis C2 of the lower mold core 130 are theoretically collinear. Furthermore, the planar portion 122 of the upper mold core 120 should be parallel to the planar portion 132 of the lower mold core 130 so that the surface of the ultimately formed optical lens 54 has no face tilting.
However, manufacturing tolerance must be allowed in fabricating the mold core and the mold so that the two can fit into each other with ease. In general, the tolerance is set between 5˜20 μm. FIG. 2 is a schematic cross-sectional view showing the structure of a conventional molding apparatus during the molding process. As shown in FIG. 2, a gap 160 is formed in the space between the upper mold core 120, the lower mold core 130 and the cylindrical mold 110. This gap 160 causes some degree of tilting in the upper mold core 120 when assembled into the cylindrical mold 110 so that the central axis C1 of the upper mold core 120 forms an included angle θ with the central axis C2 of the lower mold core 130. In other words, the planar portion 122 of the upper mold core 120 is no longer is parallel to the planar portion 132 of the lower mold core 130. Consequently, the molded optical lens 54′ will have face-tilting problem.